The mechanisms whereby integrins signal to the interior of the cell are essentially unknown. We have found a new and potentially important lead to these signaling mechanisms. We found that the intracellular protein that mediates signalling from the insulin receptor, insulin receptor substrate 1 (IRS-1) becomes associated with alpha/v integrins when cells are stimulated with insulin. This novel connection between growth factor signaling and integrins will be studied in this proposal. The first part of the study will explore the mechanism of the integrin - IRS-1 association to determine whether IRS-1 binds directly to the integrin cytoplasmic domain or whether another protein might mediate the interaction. We will also determine whether other proteins bind to the integrin - IRS-1 complex and determine the identities of such proteins, if found. We have only studied insulin so far; insulin-like growth factor (IGF) and interleukin 4 (IL-4) are also known to signal through IRS-1. We will test the ability of these two cytokines to cause the integrin association of IRS-1. Preliminary results show that the alpha/v/beta/3 integrin and probably also some other alpha/v integrins bind IRS-1, whereas beta/1 integrins have not shown any IRS-1 binding. Antibodies to various integrin subunits will be used to establish the integrin specificity of the IRS-1 association. Next, cDNA transfections, as well as cell growth, adhesion and migration assays will be used to determine how the integrin-IRS-1 association might affect insulin signaling and integrin function. The integrin-IRS-1 association is an exciting new link between integrins and growth factors that may shed light in important biological phenomena such as anchorage dependence of growth.